Source?
This is what I found after searching through Wikipedia:
Richardson asked the President if the United States was going to war. Roosevelt's view was:
At least as early as October 8, 1940, ...affairs had reached such a state that the United States would become involved in a war with Japan. ... 'that if the Japanese attacked Thailand, or the Kra Peninsula, or the Dutch East Indies we would not enter the war, that if they even attacked the Philippines he doubted whether we would enter the war, but that they (the Japanese) could not always avoid making mistakes and that as the war continued and that area of operations expanded sooner or later they would make a mistake and we would enter the war.' ... .
[5][6]
https://en.wikipedia.org/wiki/Events_leading_to_the_attack_on_Pearl_Harbor
Japan could attack the DEI without going to war with the USA. Remember, the USA was still isolationist and mostly anti-imperialist, and getting them to go to war with Japan over an
imperial possession of a foreign power? I find that hard to believe.
Japan was also not involved in unrestricted submarine warfare- meaning a direct attack on American possessions is unlikely. Japan only became public enemy No. 1 because of Pearl Harbour.
Roosevelt would much rather had the war started over the Nazis, not Japan. :/